System and method for drag reduction

ABSTRACT

A system and method for drag reduction allows thrust output, fuel efficiency or both to be maximized. Specifically, a rear portion of a body or motor vehicle may be modified to increase thrust output, fuel efficiency or both by creating a stagnation area, a suction inlet and a convex cusp area formed on the rear portion of the motor vehicle. Increasing the concavity or camber or sharpness of the radius of the stagnation area results in greater local pressure coefficient, which results in greater thrust output. The size and shape of the suction inlet and the convex cusp area will also have an effect on thrust output and fuel efficiency. A width and volume of an airplane fuselage may be increased.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 12/211,782filed on Sep. 16, 2008 which claims priority to U.S. ProvisionalApplication No. 60/960,139, filed on Sep. 17, 2007, the disclosures ofwhich are incorporated by reference herein their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to pressure thrust and morespecifically to a system and method for drag reduction, which allowsthrust output, fuel efficiency or both to be maximized.

2. Discussion of the Prior Art

The general concept of pressure thrust is known in the airfoil andaircraft design arts. The phenomenon uses energy of the air rushing pastan airplane's wing, tail surfaces or fuselage, to push that wing, tailsurface or fuselage forward. The energy required to force the freestream of airflow against the aircraft is less than the energy recoveredfrom the airflow, allowing the system to generate a decrease in totalenergy required.

In the 1940s and 1950s the Griffith Aerofoil was developed. Researchersfocused on very thick aerofoils, for use on span-loaded flying-wingtransport and they proved a meaningful decrease in total power requiredfor those designs. Fabio Goldschmied with help from Denis Bushnell atNASA uncovered and verified the pressure thrust phenomenon. The pressurethrust phenomenon is explained in Goldschmied, F. R., “AirfoilStatic-Pressure Thrust: Flight-Test Verification,” AIAA Paper 90-3286,September 1990, the contents of which are hereby incorporated byreference in their entirety.

Additional documentation concerning the pressure thrust phenomenon canbe found in Richards, E. J. and Burge, C. H. “An Airfoil Designed toGive Laminar Flow Over the Whole Surface with Boundary-Layer Suction,”A. R. C. RBM 2263, June 1943; Richards, E. J., Walker W. S. and GreeningJ. R., “Tests of a Griffith aerofoil in the 13 ft.times.9 ft. windtunnel part 1, part 2, part 3, part 4, lift, drag, pitching moments andvelocity distribution,” ARC/R&M-2148 ARC-7464 ARC-7561 ARC-8054ARC-8055, 1944 and Richards, E. J., Walker, W. S. and Taylor, C. R.,“Wind-Tunnel Tests on a 30% Suction Wing” A. R. C. RBM 2149, July 1945,Goldschmied, Fabio R., “Airfoil static-pressure thrust—Flight-testverification,” AIAA-1990-3286, AHS, and ASEE, Aircraft Design, Systemsand Operations Conference, Dayton, Ohio, Sep. 17-19, 1990. 11 p.,“Experimental investigation of a 40 percent thick half-span boundarylayer control wing,” Witte, Gerhard R., and Sullivan, John P. (PurdueUniv., West Lafayette, Ind.), Merchant, Ali, and Drela, Mark (MIT,Cambridge, Mass.), AIAA-1998-407, Aerospace Sciences Meeting andExhibit, 36th, Reno, Nev., Jan. 12-15, 1998, “Active control ofseparated flows on generic configurations at high Reynolds numbers,”Seifert A., and Pack, LaTunia G., (NASA, Langley Research Center,Hampton, Va.) AIAA-1999-3403, AIAA Fluid Dynamics Conference, 30th,Norfolk, Va., Jun. 28-Jul. 1, 1999, “Multiple Actuators Flow Controlover a Glauert-Goldschmied type Airfoil at Low Reynolds Numbers,”Yom-Tov, J. and Seifert, A., Tel Aviv University, Tel Aviv, Israel,AIAA-2005-5389, 35th AIAA Fluid Dynamics Conference and Exhibit,Toronto, Ontario, Jun. 6-9, 2005, Kummer, J. D. Dang, T. Q., “High-LiftPropulsive Airfoil with Integrated Crossflow Fan,” JOURNAL OF AIRCRAFT2006, VOL 43; NUMB 4, pages 1059-1068, Syracuse University, Syracuse,N.Y., GOLDSCHMIED, F. R. (SPERRY RAND CORP., SPERRY UTAH CO., ADVANCEDSYSTEMS DEPT., SALT LAKE CITY, UTAH), “An approach to turbulentincompressible separation under adverse pressure gradients,” Journal ofAircraft 1965, 0021-8669 vol. 2 no. 2 (108-115), PARSONS, J. S. (PurdueUniv., Lafayette, Ind.); GOODSON, R. E. (Purdue Univ., Lafayette, Ind.);GOLDSCHMIED, F. R., “Shaping of axisymmetric bodies for minimum drag inincompressible flow,” Journal of Hydronautics 1974, 0022-1716 vol. 8 no.3 (100-107), Goldschmied, Fabio R., “Aerodynamic Hull Design for HASPALTA Optimization,” Journal of Aircraft 1978, 0021-8669 vol. 15 no. 9(634-638), Goldschmied, F. R., Comment on “An Inverse Boundary-LayerMethod for Compressible Laminar and Turbulent Boundary-Layers,” Journalof Aircraft 1977, 0021-8669 vol. 14 no. 5 (509-509), Goldschmied, F. R.,“Integrated Hull Design, Boundary-Layer Control, and Propulsion ofSubmerged Bodies,” Journal of Hydronautics 1967, 0022-1716 vol. 1 no. 1(2-11), and Goldschmied, F. R., “Flow Control of Centrifugal Jet-FlapBlowers for Air-Cushion Vehicles,” Journal of Hydronautics 1980,0022-1716 vol. 14 no. 2 (48-55), the contents of which are herebyincorporated by reference in their entirety.

Further, U.S. Pat. No. 5,099,685 to McLean et al. discloses a “BoundaryLayer Control Diffuser for a Wind Tunnel or the Like” and U.S. Pat. No.5,358,200 to Onda discloses an “Airship,” which are hereby incorporatedby reference in their entirety.

Accordingly, there is a clearly felt need in the art for a system andmethod for drag reduction, which allows thrust output, fuel efficiencyor both to be maximized for suitable applications, such as vehicle bodydesign.

SUMMARY OF THE INVENTION

The present invention provides a system and method for drag reductionthat allows thrust output, fuel efficiency or both to be maximized.Specifically, a rear portion of a motor vehicle may be modified toincrease thrust output, fuel efficiency or both by creating a stagnationarea, a suction inlet and a convex cusp area on the rear portion of themotor vehicle. Increasing the concavity or sharpness of the radius ofthe stagnation area results in greater thrust output. The size and shapeof the suction inlet and the convex cusp area will also have an effecton thrust output and fuel efficiency. A width of an airplane fuselagemay be increased by creating a stagnation area, suction inlet and convexcusp area on a rear of the fuselage without a penalty to fuelefficiency.

Accordingly, it is an object of the present invention to provide asystem and method for drag reduction, which allows thrust output, fuelefficiency or both to be maximized for suitable applications, such asvehicle body design.

These and additional objects, advantages, features and benefits of thepresent invention will become apparent from the following specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of embodiments of the present invention will be apparent fromthe following detailed description of the exemplary embodiments thereof,which description should be considered in conjunction with theaccompanying drawings in which like numerals indicate like elements, inwhich:

FIG. 1 is an exemplary diagram representing a body of revolution.

FIG. 2a is an exemplary graph representing static pressure distributionwith no suction.

FIG. 2b is an exemplary graph representing static pressure distributionwith suction.

FIG. 3 is an exemplary graph representing target static pressuredistribution for a modified body.

FIG. 4a is an exemplary diagram representing a standard sedan profile.

FIG. 4b is an exemplary diagram representing a modified sedan profile.

FIG. 5a is an exemplary diagram representing labeled parts of a sedanprofile.

FIG. 5b is an exemplary diagram representing labeled profiles and partswith computed pressure coefficients shown.

FIG. 6a is an exemplary graph representing a labeled profile and partswith a computed drag coefficient shown.

FIG. 6b is another is an exemplary graph representing a labeled profileand parts with a computed drag coefficient shown.

FIG. 7 is an exemplary embodiment of a fuselage superimposed on top ofan exemplary airliner.

FIG. 8a is a diagram of a separated airflow behind a generic sedanshape, the drag coefficient for this shape was computed to be 0.34.

FIG. 8b shows a diagram of the same sedan with suction applied throughthe suction inlet at a particular flow rate and suction pressure of.

FIG. 9a is a first embodiment of a lengthwise vehicle profile tested bythe Virginia Polytechnic Institute and State University.

FIG. 9b is a second embodiment of a lengthwise vehicle profile tested bythe Virginia Polytechnic Institute and State University.

FIG. 9c is a third embodiment of a lengthwise vehicle profile tested bythe Virginia Polytechnic Institute and State University.

FIG. 9d is a fourth embodiment of a lengthwise vehicle profile with ablowing slot to exploit the Coanda effect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the spiritor the scope of the invention. Additionally, well-known elements ofexemplary embodiments of the invention will not be described in detailor will be omitted so as not to obscure the relevant details of theinvention. Further, to facilitate an understanding of the description,discussion of several terms used herein follows.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiments ofthe invention” does not require that all embodiments of the inventioninclude the discussed feature, advantage or mode of operation. Thefollowing description generally refers to FIGS. 1-9 c. For vehicles, thecurrent design is somewhat similar to the Brabham BT46B and Jim HallsChaparral 2J, both of which used engine-powered suction fans to increasedownforce. The current design goal is to use an engine-powered suctionfan(s) to decrease aerodynamic drag and, possibly, create an aerodynamicthrust force, as illustrated in FIG. 3.

Despite encouraging results from initial testing (done in the 1940s,1960s, etc.), improvements are required for the pressure thrust engineto reach its most favorable configuration. By varying the amount ofthrust and drag that are created by different parts of the design, thepower required to generate those forces and the pros and cons ofregenerative braking, as well as other variables, the entireinstallation can be optimized for any particular vehicle.

The amount of pressure thrust generated can be determined by the localpressure coefficient and the area against which that pressure acts. Thesituation for aerodynamic drag generated on the rear of the vehicle isvery much the same; pressure and area.

Generally referring to FIGS. 1-9 c, the power that may be required togenerate the target pressure distribution on the aft section(s) maydepend on a number of factors: the sharpness of the inlet radius, thesharpness of the convex-curved stagnation zone and the angle from thefree stream flow that the fluid flow must be bent so that it remainsattached across the convex stagnation area as a few non-limitingexamples. The angle from the free stream flow can be called an operatingangle or a bend angle. In one embodiment, if the installation makessizeable thrust that can be recovered by regenerative braking, thesuction power that may be required to enable that thrust may be greaterthan the power recovered, but the recovered power will reduce the totalpower requirement of the power source.

The efficiency of automotive designs at high speed is measured by thesimple Miles Per Gallon (MPG) yardstick. In one embodiment, a car orlight truck modified to exploit pressure thrust may see a similar, ifnot better-than-proven, reduction in aerodynamic drag at high speed whencompared to a vehicle not modified to exploit this phenomenon. Thepressure thrust modification can create a significant increase in MPGperformance at high speed when compared to other designs. For aircraftthe situation is similar, but may be more involved. Aircraft cruiseperformance is described by Breguet's range equation, which is wellknown in the art. Breguet's equation includes a measure of traditionalengine efficiency, namely thrust specific fuel consumption (TSFC). Forjet engines, TSFC is defined as fuel-low per pound of thrust produced(Lbm/s/lbf or kg/s/N). The variable “V” is the flight velocity and the“g” term is the acceleration of gravity. The variable “L” is lift andthe variable “D” is drag in standard aerodynamic parameters.

Breguet's classic formula illustrates the economy of power generated bythe exploitation of pressure thrust. In one embodiment, combining thefriction drag amount and either the reduced drag figure or theindependent thrust (as negative drag) with its required fuel consumptionin the range factor section of Breguet's range equation can allow theclassic aircraft performance equation to correctly measure the pressurethrust phenomenon's impact on the range factor of any given aircraft.The range factor of the range equation:V(L/D)/g(TSFC)

One important note for jetliners, however, is that transonic shock waveson the concave pressure recovery area might complicate the design. Inspite of this, these shockwaves have been shown to reduce drag on anairfoil designed by John Roncz and can be similarly exploited on afuselage. Optimizing the ratio of inlet surface area (which createsdrag) to stagnation zone surface area (thrust) can allow the modifiedgeometry to create much less pressure drag and increased pressure thrustthan does the standard Griffith/Goldschmied design known to one havingordinary skill in the art. The inlet surface area to stagnation zonesurface area ratio can be tailored to any specific problem by iterativedesign, which is a standard practice in this art.

Varying the degree of concavity may also allow the designer to tailor aStatic Pressure Coefficient, and therefore, the thrust generated, so itwill match any specific goal. Provided the fluid flow is attached, whichis a function of suction power at any given airspeed, the concavitydetermines the Static Pressure Coefficient generated.

In one exemplary embodiment, a way to measure different designs is tonote the ratio of stagnation area per unit of inlet area. Referring toFIG. 1, for the un-modified Goldschmied design, the ratio may be closeto 1/2. For an optimized design, the ratio could be far higher than 1/1.To prohibit unwanted transonic shockwaves on a jetliner fuselage, theoptimal design may have a lower ratio than an optimized automobiledesign. FIGS. 2a and 2b represent pressure distributions on the body ofa revolution depicted in FIG. 1. FIG. 2a shows a diagram for theunmodified Goldschmeid body with no suction and FIG. 2b shows it withsuction.

Quoting, Goldschmied, F. R.—Fuselage self-propulsion by static-pressurethrust Wind Tunnel Verification, AIAA 87-2935: “When the static pressurecoefficient is plotted vertically against the square of the body radiuson the horizontal scale, the nose and tail are at the left margin andthe location of maximum diameter is at the right margin. Knowing theslopes of the body, one can deduce which loops represent drag and whichrepresent thrust. Summed with integration if the surface pressuresshould give the same net drag as determined by momentum loss integrationin the wake.” Goldschmied's attempts to show this werefrustrated.—Goldschmied, F. R.—Fuselage self-propulsion bystatic-pressure thrust Wind Tunnel Verification. AIAA 87-2935, which ishereby incorporated by reference in its entirety.

FIG. 3 shows a diagram with the target pressure distribution for amodified body with the thrust area (shown on the horizontal axis,bottom) increased from roughly 38% (as measured by distance from JetNozzle to Cusp Edge, in FIGS. 1-3 above) to over 75% of total RadialArea. The benefits of decreased drag area and increased thrust area maynot depend on an increase in Static Pressure Coefficient.

Referring now to FIGS. 4a and 4b , the degree of concavity of theconcave stagnation area can determine the amount of thrust generatedprovided enough suction is used to keep flow attached. FIG. 4a disclosesa first vehicle body profile 100. FIG. 4b discloses a second vehiclebody profile 102.

Referring generally to FIGS. 5a and 5b , in one exemplary embodiment,the degree of concavity or sharpness of the radius of the stagnationarea 104 of the second vehicle body profile 102 determines the amount ofthrust generated, provided enough suction is used to keep flow attached.The need for suction power, which varies with concavity of thestagnation zone 104, may have an impact on the overall fuel efficiencyof the object. An increase in the stagnation area 104 will tend tocreate increase thrust force, with or without an increase in pressurecoefficient (Cp), because force acts on the greater stagnation area 104.Skin friction will tend to decrease Cp on the concave curve of thestagnation area 104. An increase in the camber of an airfoil will tendto increase the lift coefficient (Cl) produced; an increase in camber,bend angle or sharpness of the stagnation area 104 will tend to increaseCp and therefore increase thrust force. An inlet area 106 is formedupstream from the stagnation area 104. Optimizing dimensions of theinlet area 106 are well known in the art.

A cusp area 108 is located upstream from the inlet area 106. A shape ofthe cusp area 108 will impact performance of the inlet area 106 and thestagnation area 104. The cusp area 108 begins when a body cross-sectionreaches its greatest value and starts to decrease. Decreasing camber,sharpness, bend angle of the stagnation area 104 will tend to decreasethrust force because the stagnation area Cp is reduced. At the sametime, increased camber, “bend angle” etc., will increase stagnation areaCp, which will increase thrust force.

Varying the parameters of the stagnation area 104, the inlet area 106and the cusp area 108 will change the efficiency of a mechanismoptimized to exploit this phenomenon for a specific purpose, such asmaximum thrust or maximum fuel efficiency. The force changes andinteractions, brought about by changing these design details asdiscussed, are predictable and can be modeled so that industry standardmethods like iterative and inverse design can be used to optimize theobject or mechanism. In the hands of a person skilled in the art ofaerodynamic optimization, tools like iterative design and inverse designwill make short work of this type of optimization for any purpose.

Increasing the sharpness of the convex surface of the cusp area 108 willchange the direction of the local airflow as the airflow reaches the aftend of the convex cusp area 108 (a convex inlet of relatively low camberor sharpness will bend local airflow to a lesser degree than a convexinlet of relatively high camber or sharpness). If the concave-curvedstagnation area 104 is not designed to require or make use of localairflow that has been bent to this angle, the system efficiency will bereduced because the local airflow is bent too far. Less-than-optimalefficiency will result from local airflow that is either not bent farenough, or bent too far than the optimal amount for a specific concavestagnation zone design.

Increasing the sharpness of the convex surface of the cusp area 108 willalso allow for increased area and sharpness, bend angle or camber of theconcave stagnation area 104, which will increase the local pressurecoefficient (Cp) across the stagnation area 104. The higher pressure onthe concave curve of the stagnation area 104 will increase thrust outputcompared to thrust created by a relatively lower pressure on the concavecurve of the stagnation area 104.

Increasing the sharpness of the convex surface of the cusp area 108 willtend to increase the suction power required to keep the airflow attachedacross the concave stagnation area 104 as well as increase thrustoutput. An increase in the sharpness of the convex surface of the cusparea 108 will tend to decrease fuel efficiency as well as decrease dragas one would expect (more thrust requires more power).

Increasing the cusp area 108 will tend to decrease the area availablefor the stagnation area 104, which will tend to decrease maximumpossible thrust output. Thrust output, drag, and efficiency arefunctions of the nature of turbulent flow drag (a function of the sizeand camber of the stagnation area 104, where higher stagnation areacamber creates higher turbulent flow drag), suction power required (afunction of inlet area 106 size and camber), the local pressurecoefficient generated across the concave stagnation area 104 (a functionof stagnation zone camber and suction power) and the size of thatconcave stagnation area 104 (a function of suction system outflow size,convex inlet area size & vice versa) as well as traditional aerodynamicsubjects like separated airflow drag, etc.

An increase in the area of the cusp area 108 will create more pressuredrag (from relatively low pressure across the cusp area), but this tendsto be a much smaller force than the skin friction turbulent flow) draggenerated on the concave stagnation area 104.

A similar approach includes exploitation of the phenomenon called theCoanda effect, which is shown in FIG. 9d to maintain attached fluid flowacross the concave shape of the stagnation area.

With reference to FIG. 6a , a third vehicle body profile 110 is shown.With reference to FIG. 6b , a fourth vehicle body profile 112 is shown.The concavity of the stagnation area 114 of the third vehicle bodyprofile 110 differs from the concavity of the stagnation area 116. Bychanging the concavity of the stagnation area, the local pressurecoefficient (Cp) may also be changed and, as a result, the pressureforce may be changed, as shown by the difference in calculatedCoefficient of Drag (Cd). The fourth vehicle body profile 112 has a Cdof −0.82302 and third vehicle body profile 110 has a Cd of −0.55579. Thegreater concavity of the stagnation area 116 generates a greater thrustforce than that of the third vehicle body profile 110.

The Coefficient of Drag (Cd) is not actually negative, the ComputationalFluid Dynamics software that computed the drag coefficients stillincludes the effects of pressure in the Cd calculation. An analysis willshow that the total Coefficient of Drag has been slashed dramaticallybut that the drag forces are positive and still very real.

In yet another exemplary embodiment as shown in FIG. 7, the system andmethod for drag reduction can allow a jetliner to be much wider withoutsuffering the traditional fuel burn penalty associated with greaterfuselage area. A top view of a Boeing 737 airliner 118 is shown. A widerfuselage 120 is superimposed on top of the normal Boeing 737 airliner118. The wider fuselage 120 reveals an exemplary pressure thrustinstallation at a rear 122. The rear 122 modification includes forming acusp 124, an inlet area 126 and a stagnation area 128. An increase incamber, concavity, bend angle or sharpness of the stagnation area 128will tend to increase Cp and therefore increase thrust force. The inletarea 126 is formed upstream from the stagnation area 128. The cusp 124is located upstream from the inlet area 126. Optimizing dimensions ofthe inlet area 126 are well known in the art. The rear 122 of the widerfuselage 120 will cause that aircraft to hold more passengers than thenormal Boeing 737 airliner 118 without the penalty of increased fuelburn.

One exemplary embodiment of the invention can be summarized as follows,a high (above ambient) pressure coefficient varies with changes to slopeon concave pressure recovery area, a concave part may act much like anairfoil. The goal of wing airfoil is low pressure lift and the goal of apressure thrust airfoil is high pressure thrust.

Total thrust vs. drag performance can vary with changes to:

Drag force:

-   -   Convex Inlet area    -   Convex Inlet radius/slope/camber    -   Low pressure coefficient acting on this convex inlet        radius/slope/camber & area    -   Skin friction acting on radius/slope/camber & area of convex and        concave curved areas

Thrust force:

-   -   Concave pressure recovery area    -   Concave pressure recovery radius/slope/camber    -   High pressure coefficient acting on this radius/slope/camber &        area        Total efficiency can vary with changes to:

Suction power

Convex inlet radius/slope/camber

Inlet area

Concave stagnation zone radius/slope/camber

Concave stagnation area

Regenerative braking

Suction fan efficiency

FIGS. 8a & 8 b are diagrams from computational fluid dynamics tests runat the Virginia Polytechnic Institute and State University. FIG. 8ashows separated airflow behind the generic sedan shape 130 shown in FIG.9a . The drag coefficient for generic sedan shape 130, without suctionpower is computed to be 0.34. FIG. 8b shows the same sedan with suctionapplied through a suction inlet 134 at a suction pressure of −1130.3 Pa.The computed drag coefficient for the suction-on configuration was0.1425.

To increase thrust output from the pressure thrust installation andminimize turbulent flow drag, the designers would need to decrease thesurface area of stagnation area 132 and increase the sharpness of thebend of the stagnation area 132. Increasing the sharpness of thestagnation area 132 would increase the local pressure coefficient,similar to increasing the camber of an airfoil to increase the liftcoefficient of the airfoil. Increasing the sharpness of the stagnationarea 132 would further decrease the computed drag coefficient to apotentially negative number, which would indicate a genuine thrustcondition.

Varying the camber of an airfoil to directly change the liftcharacteristics of that airfoil is a well know mechanism, which iswidely used by aerodynamicists optimizing airfoils for a particular useor purpose. The flap systems of almost every aircraft flying aredesigned to change the camber of the airfoil so that the combination ofairfoil and extended flap create an airfoil with greater camber, so thatthe modified airfoil will be able to create a greater lift coefficientand therefore greater lift. High-lift devices are well known in the artand are widely used throughout the art.

Because the high-lift devices are well known, many skilled in the art ofairfoil design will be readily able to bring that knowledge and skill tothe task of optimizing the pressure thrust installation.

With reference to FIG. 9a , the sedan shape 130 is shown as tested byVirginia Polytechnic Institute. The sedan shape 130 includes the concavestagnation area 132, the suction inlet 134 and a convex cusp area 136.With reference to FIG. 9b , a sedan shape 138 includes most of the samebasic features of the sedan shape 130. However, a stagnation area 140includes an exaggerated camber, sharpness or “bend angle” relative tothe stagnation area 132. The geometry of the stagnation area 140 mayrequire more suction power to keep the local airflow attached, but itwill also generate more thrust, just like a wing with greater camber cangenerate more aerodynamic lift. A suction inlet 142 and a convex cusparea 144 of sedan shape 138 are similar to the suction inlet 134 andconvex cusp area 136 of the sedan shape 130.

With reference to FIG. 9c , a sedan shape 146 includes a stagnation area148, a suction inlet 150 and a convex cusp area 152. The stagnation area148 is lower than that shown in FIGS. 9 a and 9 b and smaller than theconvex cusp area 152. The suction inlet 150 is still needed. The suctioninlet 150 is sized and shaped as needed using mechanisms well known tothose skilled in the art.

Making the convex cusp area 152 greater than the stagnation area 148will not make huge differences alone. The way to create high thrustoutput is to use a relatively sharp bend (increased camber) on theconcave curve of the stagnation zone 148, and for that curve to occupy arelatively large area. Similarly, maximum efficiency will likely requirea relatively shallow bend (decreased camber) on the concave curve of thestagnation area 148 and for the concave curve to occupy a relativelysmall area.

With reference to FIG. 9d , a sedan shape 154 includes a stagnation area156, a blowing outlet 158 and a convex cusp area 160. The blowing outlet158 is needed to enable the coanda effect to bend the local airflowenough to keep it attached across the stagnation area 156. The blowingoutlet 158 is sized and shaped as needed using mechanisms well known tothose skilled in the art.

Concerning FIGS. 4-9 d, to optimize performance of an object for aparticular purpose, the designer will need to vary suction power used,the sharpness/camber and area of the inlet cusp and of the stagnationzone to achieve the particular design goal. To decrease the powerrequired by the suction pump, one would increase the size of the inletcusp and decrease the size of the stagnation zone (this will decreasethrust generated). To decrease the power required by the suction pump,one would increase the size of the inlet cusp and decrease the size ofthe stagnation zone (this will decrease thrust generated). To increasethe thrust created, one would increase the sharpness or bend or camberof the stagnation zone and/or increase the area of the stagnation zone(This will increase the suction power required). Similarly, to decreasethe turbulent flow drag, one would decrease the area of the stagnationzone. By varying these different design parameters, a designer canoptimize this system for any given purpose (i.e. Maximum efficiency, ormaximum forward thrust, etc.).

The foregoing description and accompanying drawings illustrate theprinciples, preferred embodiments and modes of operation of theinvention. However, the invention should not be construed as beinglimited to the particular embodiments discussed above. Additionalvariations of the embodiments discussed above will be appreciated bythose skilled in the art.

Therefore, the above-described embodiments should be regarded asillustrative rather than restrictive. Accordingly, it should beappreciated that variations to those embodiments can be made by thoseskilled in the art without departing from the scope of the invention asdefined by the following claims.

What is claimed is:
 1. A method for increasing efficiency of an aircraftbody moving through a fluid, comprising the steps of: forming a convexcusp area at substantially a rear of the aircraft body; extending asuction inlet and extending a stagnation area from an end of saidsuction inlet, said stagnation area having a concave shape; increasing asharpness of at least a portion of said concave shape to vary a shape ofthe stagnation area such that a local pressure coefficient across atleast a portion of the stagnation area is adjusted to increase thrustoutput; and varying at least one dimension of the suction inlet basedupon the sharpness of the at least a portion of said concave shape. 2.The method of claim 1, further comprising the step of: providing saidstagnation area with a surface area that is greater than a surface areaof said convex cusp area.
 3. The method of claim 1, further comprisingthe step of: varying said convex cusp area and said stagnation area. 4.The method of claim 1, further comprising the step of: increasing asharpness of said convex cusp area to decrease drag.
 5. The method ofclaim 1, further comprising the step of: increasing said convex cusparea to increase pressure drag.
 6. The method of claim 1, furthercomprising the step of: reducing the sharpness of said concave shape todecrease thrust output.
 7. The method of claim 1, further comprising thestep of: reducing the area of said stagnation area to reduce thrustoutput.